Defense Secretary Chuck Hagel says U.S. military commanders believe the number of U.S. troops that would remain in Afghanistan under a two-year withdrawal plan unveiled by President Barack Obama is adequate to train and advise Afghan security forces and fight terrorism.

Obama announced this week that he would leave 9,800 U.S. troops in Afghanistan when the U.S. combat mission formally ends this year.

Under the plan, the troops would be reduced by half by the end of 2015 and only a small contingent would remain by the end of 2016.

Hagel said it was not yet clear how many of the remaining U.S. troops in Afghanistan would be devoted to counterterrorism missions.

Hagel, who was heading on May 28 to Asia and Europe, said he would also visit Afghanistan during the 12-day trip.